Osteoporosis currently affects over 25 million people in the US. The majority of fractures experienced by older women are related to low bone density independent of age and therefore are osteoporotic in nature. Because calcium intake and physical activity are two modifiable behaviors associated with peak bone mass, interventions targeting these behaviors among youth have tremendous public health potential for preventing osteoporosis. Youth are particularly important to target for intervention because eating and exercise behaviors track from childhood through young adulthood. The primary aim of the proposed study is to assess the feasibility and effectiveness of a two-year behavioral program to increase calcium intake and physical activity among a cohort of fifth grade girls (age 9-11) enrolled in the Girl Scouts of St Croix Valley and Greater Minneapolis. Thirty troops will be recruited and randomized to one of two conditions: 1) eating and exercise behavior change program; or 2) no intervention control. Intervention components focus on behavioral skills development, goal setting, and self-monitoring for dietary calcium intake and physical activity, and increasing social support from peers and parents. Intervention will take place during 5th and 6th grade for ten weeks each of two years plus supporting programs during winter and summer breaks. Outcome assessments will be conducted at baseline, six, 12 and 24 months. Primary outcomes are increases over 24 months in: 1) dietary calcium intake (mg/day); 2) physical activity (minutes/week); 3) bone mineral density (mg/cm2/year). Innovative aspects of the proposed study include: 1) a unique focus on behavioral approaches to increase calcium intake and physical activity; 2) a focus on young girls in a free-living setting as they transition into adolescence; 3) an innovative, community-based intervention implemented in collaboration with the Girl Scouts Councils that could serve as a national model program for osteoporosis prevention among girls.